The invention relates to an ultrasonic sieving apparatus, and in particular to such an apparatus incorporating an ultrasonic de-coupler adapted to provide mechanical support for a transducer and resonator intended to vibrate a sieve or other separation medium.
It is well known to vibrate sieves using ultrasound for many industrial applications, and some laboratory applications. This helps prevent the sieve blinding, and therefore increases the through put of material. Typically the sieve comprises a mesh and a mesh frame in which the mesh is held under tension. A transducer is provided adjacent to the mesh in order to vibrate the mesh, typically the transducer is coupled to a resonator to improve the transmission of the vibrations to the mesh. A second resonator, for example of extended configuration, may be connected to the first resonator to increase the transmission of the vibrations to the mesh.
However, one of the main problems experienced in the prior art is providing the necessary mechanical support for the relatively heavy transducer in such a way that movement of the transducer is prevented whilst avoiding ultrasonic coupling between the transducer and the mesh frame. Such coupling is undesirable as it increases the load on the transducer and decreases the energy efficiency of the apparatus. Indeed, the increased energy input to the system to offset the inefficiency has further negative effects. For example it may cause overheating which may damage any adhesives used in the system, and it may lead to damage of the mesh. Both of these effects can reduce the serviceable lifespan of the sieve thus increasing costs of consumables and increasing downtime of the apparatus.
Various prior art sieving apparatus have incorporated de-couplers which have attempted to overcome these problems, but none are very successful and they tend to be complex in form and thus expensive to manufacture. For example, as illustrated in FIG. 1, it is known to use a cylindrical extension attached to the transducer, which has dimensions such that the resonator connected to it is connected at an anti-node in order to optimise excitation of the resonator. However, the bracket required to support the de-coupler on the mesh frame is also connected at an anti-node thus requiring the bracket to be of complex design in an attempt not to transmit the vibrations to the mesh frame.
It is an object of the invention to provide an alternative form of ultrasonic sieving apparatus comprising a de-coupler which mitigates the above described problems.